A quality assurance (QA) audit of the Trans Tasman Radiation Oncology Group and Australasian Lymphoma and Leukaemia Group trial (TROG99.04/ALLG LY02) began after accrual of 25 patients. The trial is a prospective non-randomized study of standard treatment for osteolymphoma. Data relating to informed consent, eligibility, chemotherapy and radiotherapy were reviewed. The audit showed a relatively low level ofmajor variations from the protocol, with an overall rate of 3.6%. As this trial has accrued slowly over a long period, the concept of QA has also developed. Amendments were made to the protocol accordingly. In the future, QA procedures should be predetermined, conducted rapidly in real time, and appropriately funded in order to be relevant to the ongoing conduct of the trial.